76 Minimum Window Substring

my solution

    def minWindow(self, s: str, t: str) -> str:
        req = collections.Counter(t)
        wnd = collections.defaultdict(int)
        num_kind = 0
        
        l = r = 0
        mn = float('inf')
        ml = mr = 0
        
        while r < len(s):
            if s[r] not in t:
                r += 1
                continue
            
            wnd[s[r]] += 1
            
            if wnd[s[r]] == req[s[r]]:
                num_kind += 1
            
            while l <= r and num_kind == len(req):
                if s[l] not in t:
                    l += 1
                    continue
                    
                if mn > r - l  + 1:
                    mn = r - l + 1
                    ml = l
                    mr = r

                wnd[s[l]] -= 1
                if wnd[s[l]] < req[s[l]]:
                    num_kind -= 1
                
                l += 1
            
            r += 1
        
        return s[ml:mr + 1] if mn != float('inf') else ''

 

TC

print('BANC' == Solution().minWindow('ADOBECODEBANC', 'ABC'))
print('ABA' == Solution().minWindow('ADCABCDEAKABAE', 'AAB'))
print('' == Solution().minWindow("a", "aa"))
print("ab" == Solution().minWindow("bdab", "ab"))